The invention disclosed herein is a device for determining if the ignition control module used in substantially all modern vehicles is operative to send current pulses to the primary of the engine ignition coil for starting and running the engine.
As is well known, modern automobiles have an onboard computer that sends signals to an ignition control module in which there is a transistor switch that closes the circuit to the primary of the ignition coil at the moment the spark plugs are supposed to fire. During normal engine operation, the computer may have data inputs representative of instantaneous barometric pressure, manifold vacuum level, coolant temperature, mass air flow, engine speed, and so forth. These data are used by the computer to calculate the exact instant at which the ignition spark timing signal should be sent to the ignition control module. The spark timing signal is coupled to the primary of the ignition coil through the transistor switch in the ignition control module. The transistor switch sometimes fails within itself and at other times fails to function as a result of defects in other parts of the circuitry within the ignition control module. If the transistor switch does not turn on and off in response to ignition timing signals, the engine cannot possibly start. If the engine does not start, the vehicle owner ordinarily does not have an indication as to why it does not start. Usually, however, if the transistor switch is not defective, the engine will start and any problems in engine operation must be searched for elsewhere. That is why it is important and desirable to have available an inexpensive and easy to use device for testing operability of the ignition control module as to its capability for processing an ignition timing signal from the computer and for determining if the transistor switch is operative.